nfp: bpf: improve map offload info messages

FW can put constraints on map element size to maximize resource
use and efficiency.  When user attempts offload of a map which
does not fit into those constraints an informational message is
printed to kernel logs to inform user about the reason offload
failed.  Map offload does not have access to any advanced error
reporting like verifier log or extack.  There is also currently
no way for us to nicely expose the FW capabilities to user
space.  Given all those constraints we should make sure log
messages are as informative as possible.  Improve them.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>